The invention relates to a choke coil, comprising a bead of a soft-magnetic material in which a number of ducts extend with mutually parallel axes from a first end face to a second end face in order to accommodate an electrically conductive wire having free ends, said wire forming a number of turns, each of which extends via at least two ducts.
The invention also relates to a bead and a cylindrical portion and cap suitable for use in a choke coil in accordance with the invention.
A choke coil of the kind set forth is known from Philips Components and Materials Handbook C5, Apr. 1986, FIG. 5, page 335.
In the known choke coil there is a risk of short-circuiting between the portion of the turns which projects from the bead and other conductors, for example, the tracks on a printed circuit board (PCB) or the free ends of the wire itself whereby the bead can be mounted on a PCB.
It is an object of the invention to provide a choke coil of the kind set forth in which the described drawback is mitigated. To achieve this, the choke coil in accordance with the invention is characterized in that the choke coil comprises a device for shielding a portion of the turn which extends outside the ducts.
The risk of contacting of other conductors is thus comparatively small, so that the risk of short-circuiting is strongly reduced.
A preferred embodiment of the choke coil in accordance with the invention is characterized in that the device comprises an electrically insulating housing which tightly fits around the bead and which includes an inner, approximately cylindrical portion and an outer, approximately cylindrical portion, each portion comprising a substantially closed end face on a first end portion and being axially slid over the bead with their open end portions fitting one into the other.
This is a first method of realizing the shielding. The bead and the projecting portion of the turns are shielded by the housing.
It is to be noted that the use of a housing for keeping two components together is known per se from the abstract in English of JP-A 62-245608.
A further embodiment of the choke coil in accordance with the invention is characterized in that the housing is provided with at least two openings wherethrough the free ends of the wires are fed out.
The choke coil can be mounted on a PCB by way of the free ends of the wire which are fed out Via openings in the housing.
A further embodiment of the choke coil in accordance with the invention is characterized in that the openings are provided in the end face of the cylindrical portions in the prolongation of the ducts wherefrom the free ends of the wire project from the bead.
The portions of the housing can thus be readily slid over the bead.
Depending on the desired construction of the choke coil, the free ends are fed out either via a respective opening in oppositely situated end faces of the housing or via two openings in one and the same end face of the housing.
A further embodiment of the choke coil in accordance with the invention is characterized in that an electrically insulating cap is arranged over the first end portion of each of the cylindrical portions, which cap is provided with a wire passage in the prolongation of the axis of the bead.
The wire can thus be fed out of the bead along the axis of the bead.
Another embodiment of the choke coil in accordance with the invention is characterized in that the two cylindrical portions are connected to one another by way of a snap connection.
The two cylindrical portions are thus firmly retained around the bead. The snap connection is preferably realized by cooperation between a ridge on a wall of the outer cylindrical portion which faces the inner cylindrical portion and the flared second end portion of the inner cylindrical portion.
A further embodiment of the choke coil in accordance with the invention is characterized in that the caps are secured on the first end portions of the cylindrical portions by way of a snap connection. The snap connection is preferably realized by cooperation between a ridge on a wail of the cap which faces the cylindrical portion and the flared first end portion of the cylindrical portion.
As a result, the caps are firmly attached to the end faces of the housing.
An alternative embodiment of the choke coil in accordance with the invention is characterized in that the devices formed by a recess provided in at least the first end face of the bead, which recess is situated between two ducts and interconnects the two ducts, a portion of the wire extends through the recess and the recess has a depth which is greater than the transverse dimension of the wire.
At the end face of the bead wherefrom the free ends of the wire project, the turns are situated in a recess, so that they remain fully within the bead and no longer give rise to short-circuiting.
A further embodiment of the choke coil in accordance with the invention is characterized in that the bead is provided with two diametrically oppositely situated flat faces which extend parallel to the ducts.
Because the bead comprises flat faces, it can be readily gripped for mounting on a PCB. It is to be noted that a choke coil comprising flat faces is known per se.
A further embodiment in accordance with the invention is characterized in that the axes of the ducts wherethrough the free ends of the wire project from the bead are situated in a plane substantially parallel to the flat faces. Because the free ends of the wire are situated in a plane parallel to the flat faces of the bead, the choke coil can be positioned with respect to a PCB utilizing said flat faces so that the choke coil can be automatically positioned.